Moisture-proofed plunger snap switch



Oct. 12, 1948, J. H. scr-:ELLMAN 2,451,176

vHOISTURB-PROOFED PLUNGER SNAP SWITCH Filed uarcn 27, 1945 A J(6.14;Miwg/ \\\m www ATTORNEYJ Patented Oct. 12, 1948 UNITED STATES. PATaNT.OFFICE Joseph H. Schellman, Ridley Park, Pa.; asslgnor to RobertHetherington & Son, Ine., `Wilmington, Del., a corporation of DelawareApplication- March 27, 1945, Serial No. 585.080

, 4 claims. (emot- 168)V My invention relates to switches of plungertype.

A purpose of my invention is to protect a switch from injury bymoisture.

A further purpose is to cover the press button of a switch by a moistureproof cap which is exible enough to permit the button to be pushedthrough the protecting cap and in which the cap is sealed against theswitch casing by axial clamping of the border of the cap.

A further purpose is to provide a plunger switch with a completewater-tight protection which shall not interfere with proper operationof the switch.

A further purpose is to maintain approximately atmospheric pressure uponthe switch contacts to be broken, even at high altitudes.

A further purpose is to cut off oxygen supply from switch contacts to bebroken.

A further purpose is to limit exactly the forward and rearward strokesof the plunger so as to maintain cam or wedge pressure upon a shortingbar at either or at both ends of the plunger stroke.

Further purposes will appear in the specication and in the claims.

Figure 1 is a longitudinal, central section of one form of my inventionapplied to a plunger switch, in open position. The size is greatlyexaggerated as compared with that of the present product.

Figure 1a is a fragmentary, longitudinal section of a modied form.,

Figure 2 is a section of Figure 1 taken upon line 2 2, enlarged ascompared with Figure 1.

Figure 3 is a fragmentary section corresponding generally with Figure 1,but showing to a. reduced scale the switch parts in closed position.

Figure 4 ls a front end elevation to reduced scale of the structure ofFigure 1.

In the drawings similar numerals indicate like parts.

It makes but little difference in the use of the iexibie and resilientcap or cover features of my invention as to the character of theinterior of the switch, provided the casing terminates in an outwardlyaring ilange to which the cap is clamped and, contain radially withinthis flange. an automatically retracted button, plunger or lever whichcan be operated through the flexible cover, so that the only hand ormachine operation required is the 'movement by which the switch isthrown.

The invention has been illustrated` in connection with a simple form offully operative springintention to ground the casing, this casing willxbe electrically conducting; if it is to be insulated, the material ofthe casing need not be electrical- 1y conducting; This same`threadin'gis used in applying the present invention.

The switch is held vagainst the panel between two nuts I4 and I5 inconnection with whichon one side or other of the panel, but preferablyon the forward side, a washer I8 may be used. The

'panel opening will ordinarily be threaded, in

which case the nuts will be lock nuts and in Figures 1 and 1a the washermay be a lock washer. In the figures, the front of the casing isprovided with a circular dare or ange I1 against the rear wall of whichand about which is clamped the border I`8 near the edge I9 of a ilexibleand resilient waterproof cap or cover vIl), which is preferably made ofrubber, natural or synthetic. The border at and near the edge is sprungover the ilange`s'o as by its retraction to fit within and against theinner diameters -of the ilange springing into the annular space 2iaxially back of the flange. This space has been' accentuated by groovingthe casing at 22 immediately back 4of the flange, in order to enlargethe area oi the back or rear face 23 of the flange to which the capborder is to be clamped.

i The border is clamped against the rear face of the ange by a nut 24.In Figure l the nut eective for this purpose is shown at Il'.

Clamping the cap against the ange of the outer casing effectively sealsthe front end of the switch, protecting the interior oi the cap and allwithin lt against moisture. In additionb to this mechanical clamping ofthe resilient cover to the casing, this joint between the parts isadditionally protected by bridging the. clamped joint by an insulationtype seal about what I have called a plunger 25. v another type ofswitch operating mechanism than a, direct plunger, though not to thesame advantage.

In order that I may show a complete switch operating mechanism--eventhough it be one only of many switch mechanisms that can be protected bythe cap and sealing-I describe it in connection with a plunger type ofswitch shown.

In' the structure of the figures, the body of the The cap might bethrown about `ture 88.

ing is at the rear.

vlihe body is desirably metallic. It is insulated 'at the rear by theinsulating block 83 andrearwardly-open cup insulation 8d. both withinthe bore. The forwardly facing bottom 3B of the cup closes the bore.forwardly except for aper- The two of the insulation indicated areseparate because of requirements for assemblage. The iront about the capand clampf ing nut and permissibly about theentire mount is'sealedagainst moisture by latex or synthetic rubber or other similarprotective material in the form of a coating 8l, which most desirably isvulcanized in place. A carboxyl polyvinyl chloride acetate is excellentfor this purpose.

The cup insulation is nxed in position at its front edge by shoulder 80.The rear block Si is set by engagement of the outer danse 3s with therear' end of the casing or 4 The connection between the rear block andthe casing and the connection between' the molded-in terminals 39, l andthe rear block are protected against moisture by a coating, 4i

` oflatex' or synthetic rubberor other suitable compound, which withlatex or rubber is vulcanized in place. Y

The terminals are supported by block 35 and araturned radially acrosstoward each other as at 42, 43,so as to be' connected by the front plateM of a shuttle or shortening bar 4B, mov'- ing longitudinally of the.casing within a. space et. The shorting'bar comprises said electricallyconducting front face plate Ii, apertured at el in line with aperture36. The plate is turned rearwardly at its ends I8, 48 and in rearposition of the bar, engages the front face of the block insulation bythe ends 8B, Il! to limit the rearward movement of the bar.

Both side edges B0 of-eachof the rearwardly 'turned ends .sa se arearmed, one toward the other, to constrict or at least limit the sidemovement, away from each other, of the ends El of transversely extendingparallel spiral springs 52.

'The extent of this constriction or restriction is capable of adjustmentduring assemblage by' turning the side edges to diierent extents so asto accommodate the same shorting bar size f' and construction toswitches in which the lateral pressure of the springs against the camsof a hill and valley plunger may be quite different, making it possibleby adjustment of the extent of inturning of the edges to Vmake quite aconsiderable difference in the resistances offered by the side springsto lateral ilexure of the springs by engagement of the plunger cam. v

The rear of the shuttle o r shorting bar is preferably formed by a plateof insulation, apertured at 53'.

In considering the plunger 26 above, I havev contemplated the entireplunger system, from the push button 54 to the plunger shaft 5B, whichcarries the hill and valley'v operating cam e8.

The pushbutton is externally flanged at the -rear at B1 to slide withinthe middle counterbore vand the bodyof the button is guided within thefront counterbore. k'Ihe piston-:like plunger guide l is rigid withshaft 55 and provided with a cylindrical stem 58 and front collar 80.fitting within the recess of the button and isreduced in diameter at Siat the front end so asfto ilt within the overtravel spring B2.

After the parts are assembled, the rear end of 4 the button about therecess is peened at to hold the collar within the button. Travel of thebutton il'rst moves the plunger stem against the resistance of theretraction spring Bil until the plunger is stopped.

This movement of the plunger must be enough to'pass the crest of thehill and valley cam between the centers 'of the shorting bar springs,causing the snorting bar to shift forwardly and close the switch. Travelof the button beyond the point at which the plunger stops causescompression of the overtravel spring 62 to begin. The crest of thedouble cam Se is located at the point where the two truncated cones cometogether,

base to base. The slopes of'I the two cams are diierent.

During movement of the plunger rearwardly, to' cause forward (switchclosing) movement of the ehorting bar, when the double cam is pushed sothat the crest of the cam passes downwardly, rearwardly in Figure 2,past the plane between the center lines of the snorting bar springs, thesnorting .bar lshifts forwardly and travels down the long forwardlyfacing slope to closure, giving a relatively slow movement and providingconveniently for overthrow of the plunger after the snorting .bar hasbeen seated against the contacts.

j On the retraction stroke the piston-like guide engages'the shoulder 3iat the front end of the guides travel, preventing excessive forwardtravel of the stem.

The plunger shaft is guided at its rear end by i vthe walls of therecess 6d whose bottom 66 can be used to limit the extent of travel ofthe plunger. The travel can be limited also by complete compression ofthe retraction spring or, where the s'eat of the spring is deep enoughto permit the spring to compress within it, the travel can be limited byengagement of the rear face 51 of the pistonlike guide with the frontface 68 of the cupped insulation.

. Positivev limitation of the rearward movement of the plunger shaftpermits the shaft to be stopped reliably while the snorting bartransverse springs are still engaged by the front slope of the hill andvalley cam, thus maintaining ypressure upon the snorting bar to hold itrmly against the contacts 42 and 43, holding the switch closed.

. Both of the means for limiting the plunger stroke stop it where thepiston-like guideengages the shoulder at 3|. On the rear stroke theplunger is stopped by the bottom of the guide opening. g Completeprotection against moisture, involving as it does complete protectionagainst admission and outward ow to and from the interior of the switchhas several distinct advantages. Wherever used the maintenance of a uniform atmosphere about the arc is quite desirable, not only as regardsthe moisture, but as regards the oxygen content. Where the space isclosed, the oxygen is soon completely burned out leaving an inert gasin-which ythe spark cannot nd fuel.

When the switch is surrounded by raried atmosphere,` as in high altitudeairplane use, the inert gals, even without its oxygen content, maintainsa pressure within the enclosure greatly in excess of the pressure of thesurrounding air and which is maintained at nearly the same reducedpressure by the resistance of the cap expansion.

The protection against moisture means also form upon the contacts. Italso avoids ignition actieve of dangerous gases by contact of the gaseswith the switch arc.

. When the rubber cap is slightly collapsed dur ing the pushing of theplunger from the outside of the cap, the pressure about the hill andvalley switch contacts is relatively slightly increased, this additionalpressure is maintained while arcing takes place. At high altitudes theone pushing upon the button through the rubber cap thus slightlycorrects and makes more nearly normal the pressure at the time theswitch is closed and hence continues to maintain the higher pressureduring the time when the push button pressure is released and at thebeginning of which releas.

ing the arc is made.

It will be evident that various forces are at worl; in determining theconditions inside of the switch. This pressure will be less in raririedatmospheres because the outside pressure is very much less than theapproximately 15 pounds pressure per square inch at normal atmosphericpressure.

The reduction in pressure is offset by the resistance of the capmaterial to stretching, by the burning out of the oxygen from theatmosphereon the other hand it is increased by the reduction of volumeof the space inside of the switch by collapse of the cap when theplunger is thrown rearwardly, which relative compression continues whenthe button is released and the switch is opened.

it is to be noted that on the reverse movement, when the pressure uponthe push .button is released the short and relatively steeprearwardlyfacing slope of the came becomes effective.

h1 Figure le the cap and the manner oi' cap fastening as well asthe'structure inside the casing is intended to be the same asthat shownin Figure l. The casing is flared and grooved and externally threaded,as in Figure 1, the only difference being in the manner of theattachment to the panel. In this case the panelis not threaded, the capis held in place by a nut I4' threaded upon the casing and compressingthe border end of the cap adjacent its edge.

When the acetate is used the sealing material is not vulcanized.

VThe forwardly facing slope of the hill and valley switch is moregradual (i. e. less steep). than the rearwardly facing slope. At the'switch c105- ing end of the shorting bar movement, the springs 62 restupon the forwardly facing slope so u to maintain forward pressure uponthe shox-ting bar to keep the contact nrmly closed.

In view of my invention and disclosure varia.-

tions and modlncations to meet individual whim switch having a threadedexterior and an outwardly :flaring ange upon the front and aspringretracted operating member moving forward and baci: at the front,a waterproof, flexible and elas- I tic cup surrounding the iange andoperating member-and engaging the rear of the flange and a nut mountedupon the casing and pressing the edge of the cup against the rear of thenange.

2. In a switch, a casing having a threaded ex? terior flanged at thefront, a resilient, moistureprooi cap of smaller edge circumference thanthat oi' the inside of the front ange, a nut mounted by the casing,axially engaging the edge of the cap and pressing it tightly axiallyagainst the rear lace of the flange and switch mechanism terminating inan operating plunger within the cap, adapted to be operated from theoutside through the cap, thus taking advantage of the exure of the cap.

3. In a switch', an automatically retractable switch having a threadedexterior and an outwardly flaring ange upon the front and aspringretracted operating member moving forward and back at the front, awaterproof, flexible and elastic cup surrounding the ange and operatingvmember and engaging the rearl of the nance, a

nut mounted upon the casing and pressing the edge of the cup against therear of the flange. and a waterproof coating extending from the nut tothe cup and over the joint between the nut and the cup to seal the same.l

i. In a switch, a cas vhaving a threaded er1- terior flanged on theiront, a resilient, moistureproof cap of smaller edge circumfere thanthat of the inside of the iront iiange, e, nut mounted on the casing,axially engaging the edge of the cap, and pressing it tightly axiallyagaimt the rear face of the harige, switch mechanism ter minating in anoperating plunger within the cap, adapted to be operated from theoutsidethrough the cap, thus taking advantage of the flexure of the cap,and a. waterproof coating of vulcanizable material extending over theoutside of the nut and over the cap, sealing the joint between the nutand th'e cap and vulcanized in place.

JOSEPH H. SCHELLMAN.

REFERENCES The following references are of record in the me of thispatent:

STATES PATENTS Number Name Date 450,292 Johnston Apr. 14, 1891 809,262Hood Jan. 2, 1908 1,222,214 Klein Apr. 10, 1917 1,837,185 Jones Dec. 15,1981 2,202,207 Johnson May 28, 1940 2,301,874 Hetherington Nov. 10, 19422,367,441 Schwinn Jan. 15, 1945 2,388,162 Hetherington Oct. 2. 1945FOREIGN PATENTE Number Country i Date 198,595 Germany Dec. 18. 1907

